UK government has urged to de-escalate tensions in the Gulf by releasing a British-flagged ship that said, it had been illegally seized in Omani waters in an “utterly unacceptable” gambit on Sunday.

Tehran was defiantly ignoring mounting European appeals to free the captured oil tanker and its mostly Indian crew, as the United States prepared to redeploy troops to Iran’s regional arch-rival Saudi Arabia.

Iran’s Islamic Revolutionary Guard Corps (IRGC) said that ” it seized the Stena Impero ship on Friday for breaking “international maritime rules” in the Strait of Hormuz, a Gulf chokepoint for about a third of the world’s sea-borne oil”.

According to Iranian authorities, “The oil tanker was impounded off Bandar Abbas port for allegedly failing to respond to distress calls and turning off its transponder after colliding with a fishing vessel”.

18 Indians are among the 23 crew in the British-flagged oil tanker seized by Iran, the Ministry of External Affairs on Saturday said that the government was in touch with the Iranian government to secure the early release and repatriation of Indian nationals, a report stated.

Eighteen Indians, including the captain, and nationals from the Philippines, Latvia and Russia were on board the Stena Impero when Iran’s Revolutionary Guards Corps (IRGC) seized the tanker in the Strait of Hormuz on Friday for breaking “international maritime rules” as tensions mount in the highly sensitive waterway.

“The British vessel was captured for failing to respect the international maritime rules while passing through the Strait of Hormuz,” said a statement released by Public Relations of the IRGC.

British Foreign Secretary Jeremy Hunt said, “They see this as a tit-for-tat situation,” while meeting with Iran Foreign minister Mohammad Javad Zarif.

Hunt further said that while the Grace 1 had been detained legally, “the Stena Impero was seized in Omani waters in clear contravention of international law. It was then forced to sail into Iran. This is totally and utterly unacceptable.”

However, the other ship, the Liberian-flagged Mesdar was set free after it was temporarily boarded by armed personnel, the owner of the tanker said.

Meanwhile, Iran has opened an investigation into the tanker as it alleged that the ship collided with a fishing vessel in the Strait of Hormuz.

The incident came as Iran’s Islamic Revolutionary Guard Corps (IRGC) announced that it had seized a foreign ship “smuggling fuel” in the Gulf on Thursday, days after reports of a British tanker being harassed in the region.

Tensions spiked last month when Iran shot down a US drone over sensitive Gulf waters following a series of oil tanker attacks that Washington blamed on Tehran, which the latter denied.